UV Unwrapping complex drilled cube
Hit Shift+G in Edit mode while having one of the edges selected that you want to mark as a seam.

This brings up the select similar dialog which offers the possibility to select other elements by similar properties (in your example perhaps edge length)

Another way to speed things up is box selection (B) in edit mode or circle selection (C) in edit mode. If you want to get certain stuff out of the way while selecting hit H to hide elements. Just make sure you unhide them before you unwrap.